Photoelectric device for measuring the spectral line intensities of a radiating plasma with background radiation correction means



May 2, 1967 M. KPSEL ETAL PHOTOELECTRIC DEVICE FOR MEASURING THE SPECTRAL LINE INTENSITIES OF A RADIATING PLASMA WITH BACKGROUND RADIATION CORRECTION MEANS l5 Sheets-Sheet 1 Filed Nov.

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May 2, 1967 M. KPSEL ETAL 3,317,737

PHOTOELECTRIC DEVICE FOR MEASURING THE SPECTRAL LINE INTENSITIES OF' A RADIATING PLASMA WITH BACKGROUND RADIATION CORRECTION MEANS May 2 1967 M. KPSEL ETAL 3,317,737

PHOTOELECTRIC DEVICE FOR MEASURING THE SPECTRAL LINE INTENSTIES OF A RADIATING PLASMA WITH BACKGROUND RADIATION CORRECTION MEANS l5 Sheets-Sheet 5 Filed Nov. 5, 1963 I N VE NTQRS May 2, 1967 M. KPsr-:L ETAL 3,317,737

PHOTOELECTRIC DEVICE FOR MEASURING THE SPECTRAL LINE INTENSITIES OF A RADIATING PLASMA WITHV BACKGROUND RADIATION CORRECTION MEANS Filed Nov. 5, 1963 13 Sheets-Sheet 4 May 2, 1967 M. KPSEL ETAL 3,37737 PEOTOELECTRIC DEVIGEFOR MEASURING THE SPECTRAL LINE INTENSITIES OF A RADIATING PLASMA WITH BACKGROUND RADIATION CORRECTIGN MEANS Filed Nov. 5, 1963 13 Sheets-Sheet 5 /oooo /sooo :aoco zsooo vc rE/vfaewrl/ef INVEN O Mms/mvo /egz ay 2, W67 M. KPSEL ETAL. 3,317,737

PHOTOELECTRIC DEVICE EOE MEASURTNC TEE sPECTRAL LINE INTENsITIEs OE A RAOTATING PLASMA WITH BACKGROUND RADIATION CORRECTION MEANS Filed Nov. 5, 1963 13 Sheets-Sheet 6 /oooo /5000 20000 25000 'K 7`MPEA7 T086 Eig-E may 2, i967 M. KPSEL ETAI. 3,377737 PHOTOELECTHIC DEVICE FOR MEASURING THE SPECTRAL LINE INTENSITIES OF A RADIATING PLASMA WITH BACKGROUND RADIATION CORRECTION MEANS Filed Nov. 5, 1963 13 Sheets-Sheet 7 #ne Phys/17,9: /vz A :4s/S L//vf /frrews/ ry @Y 2, 'i967 M. KPSEL ETAL 3,37737 PHOTOELECTRIC DEVICE FCE MEASURING THE SPECTRAL LINE INTENSITIES 0F A EADIATINC PLASMA WITH BACKGROUND RADIATION CORRECTION MEANS Filed Nov. 5, 1963 13 Sheets-Sheet 8 7E MP6" 197' 019 1N VENTORS may 2 i967 M. KPSEL. ETAT. 3,337,737

PROTODLECTRIC DEVICE FOR NEASURING THR SPDCTRAL LINE INTRNSITIES OR A RADIATINC PLASMA WITH BACKGROUND RADIATION CORRECTION MEANS Filed Nov. 5, 1963 13 Sheets-Sheet 9 /oaoo 15000 20000 25000 'k May 2, i967 M. KPSEL ETAL PHOTOELECTRIC DEVICE FOR MEASURING THE SPECTRAL LINE INTENSITIES OF A RADIATING PLASMA WITH BACKGROUND RADIATION CORRECTION MEANS Filed NOV. 5, 1963 l5 Sheets-Sheet lO Fig-1Q INVENTORS /V/w-:efa kan sez droLL,

ay 2, i6? M. KPSEL ETAL 3,37737 PHOTOELECTRIC DEVICE FOR MEASURING THE SPECTRAL LINE INTENSITIES OF A RADIATING PLASMA WITH BACKGROUND RADIATION CGHRECTION MEANS Filed Nov. 5, 1965 13 Sheets-Sheet l1 TEM P 6R19 70,96

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May 2, w67 M. KPsr-:L ETAL 3331737 PHOTOELECTRIC DEVICE FOR MEASURING THE SPECTRAL LINE INTENSITIES OF A RADIATING PLASMA WITH BACKGROUND RADIATION CORRECTION MEANS Filed Nov. 5, 1965 l5 Sheets-Sheet l2 ant/H [elm aut/77 TMP 619/9 Tl/r? 6 May 2, 1967 M. KPsI-:L ETAL 3,337,737

PROIOELECTRIO DEVICE ROR MEASURING TRE sPEcTRAL LINE INTENsITIEs OE A RADIATINO PLASMA WITH BACKGROUND RADIATION CORRECTION MEANS Filed Nov. 5, 1963 13 Sheets-Sheet l5 l @uw gif /oooo /saaa 20000 2 sooo '/1 rf/vae' ra@ .f -hv- INVENTORS E 1 gj l @my ,ef/2R52? United States Patent O 3,317,737 PHGTOELECTRIC DEVICE FOR MEASURING THE SPECTRAL LINE INTENSITIES F A RADIAT- ING PLASMA WITH BACKGROUND RADIATIN CORRECTION MEANS Manfred Kpsel, Neumunster, and Johannes Richter and Walter Lochte-Holtgreven, Kiel, Germany, assignors to the United States of America as represented by the Secretary of the Air Force Filed Nov. 5, 1963, Ser. No. 321,704 2 Claims. (Ci. Z50- 226) The invention relates to a device for measuring the spectral line intensities of a radiating plasma from which the temperature can be determined.

One object of the invention is to provide a device for subtracting the gackground illumination from the spectral line intensities of a radiating plasma wherein only a single photomultiplier is required.

Another object is to provide a device for subtracting the background illumination from the spectral line intensities of a radiating plasma wherein the intensity is given as an instantaneous reading on a meter.

The foregoing objects are achieved by providing a mirror arrangement with a narrow band spectrometer, wherein the mirror is used to sweep the spectral line and the backoround in the output of the narrow band spectrometer across a slit in front of a photomultiplier. The output of the photomultiplier is gated to apply the signal responsive to the spectral line to one terminal of a meter and to alternately apply a signal responsive to the background on both sides of the spectral line to the other terminal of the meter.

These and other objects will be more fully understood from the following detailed description taken with the drawing wherein: I

FIG. 1 shows a line prole of the spectral intensity vs. wavelength for one spectral line and the adjacent background with the slit positions at the time of switching indicated;

FIG. 2 is a diagrammatic showing, partially in block form, of the device of the invention;

FIG 3 is a circuit schematic of one possible amplier and gate circuit for the device of FIG. 2;

FIG. 4 is a circuit schematic for a timing pulse genera tor and gate pulse generator circuits which may be used with the device of FIG. 2;

FIG. 5 is a circuit schematic for a 2O c.p.s. oscillator which may be used with the device of FIG. 2;

FIGS. 6-15 show intensity-temperature curves as a function of pressure in an atmospheric plasma.

The temperature of a radiating plasma can be determined from the spectral line intensities. For an exact line intensity measurement, the integral over the spectral intensity of the line has to be determined. This integral is given by the shaded `area under the line profile shown above the dotted line in FIG. l of the drawing. Thus it is seen that the area under the dotted line due to background must be subtracted from the total intensity or" the line plus background to obtain the spectral line intensity.

Certain prior art systems have arrangements for doing this for two exit slits, one on the line and one on the background near the line. Such a system requires the use of two photomultipliers with their inherent dilierent characteristics which produce errors and also will only work if the background is substantially dat.

According to this invention, a mirror arrangement is used which sweeps the spectral line and background across an output slit. A photomultiplier is located behind the slitand has its output gated so that a more accurate line intensity value is provided even in the case where the background radiation has a linear wavelength dependence,

3,317,737 Patented May 2, 1967 as shown in FIG. 1 by alternately subtracting the signal due to background on both sides of the spectral line.

As shown in FIG. 2, light from a plasma source, generally indi-cated at 10, is imaged upon the entrance slit S1 of a narrow band spectrometer or monochromator 15 by means of a mirror 11, a prism 12, `and lenses 13 'and 14. The mirror 11 can be moved to an alternate position 2 so that lenses 14 and 16 focus light from a standard source 17 at the entrance slit S1. The monochromator 15 is a standard Bausch and Lomb type (33-86-45-01) grating monochromator with grating of 600 grooves/ mm. Filters or diaphragms such as shown schematically at 18, may be provided when needed for reducing the light intensity or the solid angle and cutting out dispersed light and may be located between lens 14 and prism 12.

An oscillating mirror 20 is located behind the monochromator output slit S2. A lens 21 forms the image of slit S2 on the mask 23 having an output slit S3. A photomultiplier 24 receives the light passing slit S3.

The mirror 20, lens 21, mask 22, and photomultiplier 24 are housed in an opaque housing 26.

The output of the photomultiplier 24 is applied to an amplier 39, shown in greater detail in FIG. 3, and then to a measuring instrument 31 through gate circuits 32 and 33, shown in greater detail in FIG. 3.

A 20 c.p.s. oscillator 35, shown in greater detail in FIG. 5, supplies a 20 c.p.s. signal to the timing pulse generator 37 and to the mirror drive 38. The timing pulse generator has a variable delay so that the phase of the output pulses to gate pulse generators 40 and 41 may be controlled. The gate pulse generator 40 applies a 3 msec. gate pulse to gate circuit 32 when the mirror 2t) is at either of its maximum deflection positions. The gate pulse generator 41 applies a 3 msec. pulse to the gate cir cuit 33 when the mirror 20 passes through its center position. Thus the signal from amplifier 3) is applied to the measuring instrument 31 through gate 32 for the times indicated as A and C in FIG. 1 and through gate 33 for the time indicated as B in FIG. l. Since the signal due to background light on both sides of the spectral -line is subtracted in the measuring instrument, a more accurate intensity measurement is provided. The circuits for the timing pulse generator and gate pulse generators are shown in FIG. 4. The 20 c.p.s. signal from oscillator 35 is applied to trigger circuit 45 which applies a trigger pulse to monostable multivibrators 46 and 47 once each cycle. Thus a trigger pulse is applied to multivibrators 46 and 47 from the trigger circuit every 50 msec. The delay time of multivibrator 46 is set to equal 25 msec. so that multivibrator 47 receives a pulse either from trigger circuit 45 or multivibrator 46 every 25 msec. The delay time of multivibrator 47 may be adjusted by means of variable resistor 48 to change the delay between 0 and 2) msec. so that the gate Ipulses can be synchronized with the oscillating mirror. An oscilloscope may be used for synchronizing the device. It is obvious that circuits other than those shown may be used. The measuring instrument used is a standard MA. meter.

In the operation of the device of the invention the mirror 11 is located in position 2. The plasma light source is then focused at the slit S1. A spectral line suitable for good temperature measurement is selected by the monochromator. The width of slit S1 is set equal to L.W./D. where LW. equals line Width and D equals the dispersion of the monochromator which for the device used is 33 A./mm. In any case, the width of the slit should not be set less than 0.03 mm. Slit S2 is opened wide. Slit S3 is made equal to 3S1. The oscillating mirror amplitude is adjusted by 39 and multimeter 42 to about 6S1 at the slit plane of S3.

The intensity of the plasma source AL is then read on the meter in terms of the meter scale. To obtain an absolute intensity measurement, the mirror 11 is adjusted to position 2 and slit S2 is made equal t0 slit S1. The intensity of the carbon arc AC for the line wavelength is then read on the meter. The intensity of the spectral line is then obtained from the following expression:

where 1=total line intensity E,=spectral line intensity of carbon arc D=dispersion of monochromator 33 A./mm. S2=width of slit S2 (mm.)

wherein E is obtained by using the table which follows:

Wavelength, Intensity, Wavelength, Intensity,

A. erg/seocm.3 A. erg/seocm.a

ster. ster.

OI 3947 0. 9130-1013 NI 5412 2. 491013 4000 1. 05-10111 5500 2. 561013 4100 1. 161013 5600 2. 63-1013 4200 1. 27-1013 NH 5680 2. (iS-1013 4300 1, 384013 5700 2. 70-1013 OI 4368 1. 461013 580() 2. 76-1013 4400 1. 491013 5900 2. 821013 4500 1. 601013 6000 2. 87-1013 4600 1. 71-1013 6100 2. 921013 NII 4631 1. 75101a OI 6157 2. 95-1013 4700 1. 82-1013 6200 2. 07-1013 4800 1. 93-1013 6300 3. 01-1013 4900 2. 034013 G400 3. 05-1013 NI 4915 2. 04-1013 6500 3. 0214013 NI 4935 2. 001013 6600 3. -1013 5000 2. 13-1013 6700 3. 12-1013 5100 2. 2310111 6800 3. 14-10111 5200 2. 3l-1013 6900 3. 15-1013 The intensity lper cm. of length of the owing plasma I AL E). ITAC' L 'D52 From this value the temperature for an air plasma can be determined from the charts shown in FIGS. 6-15.

The temperature for other plasmas may be determined from the value I/ L in the manner known in the prior art.

There is thus provided a device for providing a more 'accurate spectral line intensity measurement.

While a specific embodiment of the invention has been described in detail, it is obvious that numerous changes may be made without departing from the general principle and scope of the invention.

We claim:

1. A device for measuring the spectral line intensities of light from a radiating plasma; comprising, -a narrow band spectrometer having an input slit and an output slit; means for focusing the radiating plasma on the input slit of said narrow band spectrometer; a light-tight housing adjacent the output slit of said narrow band spectrometer; a photomultiplier within said housing; means, including an oscillating mirror, within said housing, for impressing the light from said output slit on said photomultiplier; means for driving said oscillating mirror at a predetermined frequency; a mask, having a slit therein, located between said oscillating mirror and said photomultiplier;

a measuring instrument having at least two input terminals; a rst circuit means, including a gate circuit, for connecting the output of said photomultiplier to one terminal of said measuring instrument; a second circuit means, including a gate circuit, for connecting the output of said photomultiplier to the other terminal of said measuring instrument; means responsive to the means for driving said mirror at a predetermined frequency, Vfor closing the gate in said rst circuit for a predetermined time interval when said mirror is in either of its maximum deection positions; means, responsive to the means for driving said mirror at a predetermined frequency, for closing the gate in said second circuit for a time equal to said predetermined time interval when said mirror is in its equiiibrium position; and means for providing a reference intensity indication on said measuring instrument.

2. A device for measuring the spectral line intensities of a radiating plasma; comprising, a narrow band spectrometer having -an input slit and an output slit; means for focusing the radiating plasma on the input slit of said narrow band spectrometer; a light-tight housing adjacent the output slit of said narrow band spectrometer; a photomultiplier within said housing; means including a mirror within said housing, for impressing the light from said output slit on said photomultiplier; means for deiiecting said mirror through a predetermined angle at a predetermined frequency; a mask, having a slit therein, located between said mirror and said photomultiplier; a measuring instrument having vat least two input terminals; a rst circuit means including a gate circuit for connecting the output of said photomultiplier to one terminal of said measuring instrument; a second circuit means, including a gate circuit, for connecting the output of said photomultiplier to the other terminal of said measuring instrument; means responsive to the means for deecting said mirror .at a predetermined frequency, for producing a rst gate pulse covering a predetermined time interval corresponding to the time when said mirror is in either of its maximum deilection positions; means for applying said rst gate pulse to the gate circuit in said rst circuit, to thereby apply the output signal of said photomultiplier responsive to the background intensity of the light to said measuring instrument; means, responsive to the means for deflecting said mirror atV a predetermined frequency, for producing a second gate puise covering a time equal to said predetermined time interval corresponding to the time when said mirror is in its equilibrium position; means for applying said second gate pulse to the gate circuit in said second circuit, to thereby lapply the ouput signal of said photomultiplier, responsive to the intensity of the spectral line, to said measuring instrument; and means for providing a reference intensity indication on said measuring instrument.

References Cited by the'Examiner UNITED STATES PATENTS 2,406,318 8/1946 Brace 250-226 X 2,630,736 3/1953 Beitz 250,-235 X 3,004,465 10/1961 White 88-14 RALH G. NILSON, Primary Examiner.

J. D. VWALL, Assistant Examiner. 

1. A DEVICE FOR MEASURING THE SPECTRAL LINE INTENSITIES OF LIGHT FROM A RADIATING PLASMA; COMPRISING, A NARROW BAND SPECTROMETER HAVING AN INPUT SLIT AND AN OUTPUT SLIT; MEANS FOR FOCUSING THE RADIATING PLASMA ON THE INPUT SLIT OF SAID NARROW BAND SPECTROMETER; A LIGHT-TIGHT HOUSING ADJACENT THE OUTPUT SLIT OF SAID NARROW BAND SPECTROMETER; A PHOTOMULTIPLIER WITHIN SAID HOUSING; MEANS, INCLUDING AN OSCILLATING MIRROR, WITHIN SAID HOUSING, FOR IMPRESSING THE LIGHT FROM SAID OUTPUT SLIT ON SAID PHOTOMULTIPLIER; MEANS FOR DRIVING SAID OSCILLATING MIRROR AT A PREDETERMINED FREQUENCY; A MASK, HAVING A SLIT THEREIN, LOCATED BETWEEN SAID OSCILLATING MIRROR AND SAID PHOTOMULTIPLIER; A MEASURING INSTRUMENT HAVING AT LEAST TWO INPUT TERMINALS; A FIRST CIRCUIT MEANS, INCLUDING A GATE CIRCUIT, FOR CONNECTING THE OUTPUT OF SAID PHOTOMULTIPLIER TO ONE TERMINAL OF SAID MEASURING INSTRUMENT; A SECOND CIRCUIT MEANS, INCLUDING A GATE CIRCUIT, FOR CONNECTING THE OUTPUT OF SAID PHOTOMULTIPLIER TO THE OTHER TERMINAL OF SAID MEASURING INSTRUMENT; MEANS RESPONSIVE TO THE MEANS FOR DRIVING SAID MIRROR AT A PREDETERMINED FREQUENCY, FOR CLOSING THE GATE IN SAID FIRST CIRCUIT FOR A PREDETERMINED TIME INTERVAL WHEN SAID MIRROR IS IN EITHER OF ITS MAXIMUM DEFLECTION POSITIONS; MEANS, RESPONSIVE TO THE MEANS FOR DRIVING SAID MIRROR AT A PREDETERMINED FREQUENCY, FOR CLOSING THE GATE IN SAID SECOND CIRCUIT FOR A TIME EQUAL TO SAID PREDETERMINED TIME INTERVAL WHEN SAID MIRROR IS IN ITS EQUILIBRIUM POSITION; AND MEANS FOR PROVIDING A REFERENCE INTENSITY INDICATION ON SAID MEASURING INSTRUMENT. 